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| United States Patent |
6,013,324
|
|
Frangou
, et al.
|
January 11, 2000
|
Coating composition
Abstract
A sprayable aqueous coating composition for motor vehicles comprising an
aqueous dispersion of addition polymer microparticles having a crosslinked
core and a non-crosslinked stabilising mantle containing acid groups,
characterised in that the crosslinked core comprises: i) a crosslinked
inner core of an addition polymer and ii) a crosslinked outer core of
addition polymer which is made from at least 10% by weight of monomers
having a solubility in water of less than 0.1% by weight ratio of the
inner core to the outer core being in the range 10:90 to 90:10.
| Inventors:
|
Frangou; Andrew (Windlesham, GB);
Casper; James William (Stokenchurch, GB);
Gogna; Deepak (Slough, GB);
Highcock; William James (Farnham Common, GB)
|
| Assignee:
|
Imperial Chemical Industries PLC (London, GB)
|
| Appl. No.:
|
091002 |
| Filed:
|
July 30, 1998 |
| PCT Filed:
|
December 11, 1996
|
| PCT NO:
|
PCT/EP96/05534
|
| 371 Date:
|
July 30, 1998
|
| 102(e) Date:
|
July 30, 1998
|
| PCT PUB.NO.:
|
WO97/22667 |
| PCT PUB. Date:
|
June 26, 1997 |
Foreign Application Priority Data
| Current U.S. Class: |
427/388.4; 427/407.1; 523/201; 523/406; 524/458; 524/501; 524/522; 524/523; 525/309; 525/902; 526/273 |
| Intern'l Class: |
B05D 001/36; B05D 007/16; C08F 024/00; C08F 265/04 |
| Field of Search: |
427/388.4,409,388.2,407.1
523/201,406,221
525/902,309
526/273
524/517,515,458,501,522,523
|
References Cited
U.S. Patent Documents
| 3787522 | Jan., 1974 | Dickie et al.
| |
| 4086300 | Apr., 1978 | Owens et al.
| |
| 4540740 | Sep., 1985 | Olson et al. | 524/811.
|
| 4569966 | Feb., 1986 | Piccirilli et al. | 524/589.
|
| 4730023 | Mar., 1988 | Sato et al. | 525/73.
|
| 4849480 | Jul., 1989 | Antonelli et al. | 525/303.
|
| 5219900 | Jun., 1993 | Davies et al. | 523/201.
|
| 5346958 | Sep., 1994 | Yuakwa et al. | 525/124.
|
| 5412039 | May., 1995 | Barsotti et al. | 525/309.
|
| 5763528 | Jun., 1998 | Barsotti et al. | 525/63.
|
| Foreign Patent Documents |
| 348 565 | Jan., 1990 | EP.
| |
| 667 360 | Aug., 1995 | EP.
| |
| 2 069 007 | Mar., 1971 | FR.
| |
| 1 179 331 | Jan., 1970 | GB.
| |
Primary Examiner: Dudash; Diana
Attorney, Agent or Firm: Pillsbury Madison & Sutro LLP
Claims
We claim:
1. A sprayable aqueous coating composition for motor vehicles comprising an
aqueous dispersion of addition polymer microparticles having a crosslinked
core and a non-crosslinked stabilising mantle containing acid groups,
characterised in that the crosslinked core comprises;
i) a crosslinked inner core of an addition polymer and,
ii) a crosslinked outer core of addition polymer which is made from at
least 10% by weight of monomers having a solubility in water of less than
0.1% by weight,
the weight ratio of the inner core to the outer core being in the range
10:90 to 90:10, the mantle having a Tg of -50.degree. C. to +50.degree.
C., and being made from 5 to 19% by weight of monomers having acid groups.
2. A coating composition as claimed in claim 1 in which the monomers having
a solubility in water of less than 0.1% by weight are selected from
2-ethylhexyl acrylate, styrene and mixtures thereof.
3. A coating composition as claimed in claim 1 in which the monomers having
a solubility in water of less than 0.1% by weight comprise styrene.
4. A coating composition as claimed in any one of claims 1 to 3 in which
the outer core polymer has a Tg of at least 5.degree. C. greater than the
Tg of the inner core polymer.
5. A coating composition as claimed in any one of claims 1 to 3 in which
the outer core has a Tg of greater than 10.degree. C.
6. A coating composition as claimed in any one of claims 1 to 3 in which
the outer core is made from at least 15% by weight of monomers having a
water solubility of less than 0.1% by weight.
7. A coating composition as claimed in any one of claims 1 to 3 in which
the outer core is made from monomers selected from methyl methacrylate,
butyl acrylate, 2-ethylhexyl acrylate, styrene and allyl methacrylate and
mixtures of these.
8. A coating composition as claimed in any one of claims 1 to 3 in which
the inner core has a Tg of less than -10.degree. C.
9. A coating composition as claimed in any one of claims 1 to 3 in which
the inner core is made from monomers selected from methyl methacrylate,
butyl acrylate, styrene and allyl methacrylate and mixtures of these.
10. A coating composition as claimed in claim 1 in which the outer core and
the inner core have the same monomer composition.
11. A coating composition as claimed in any one of claims 1 to 3 in which
the mantle is made from 3 to 30% by weight of monomers having acid groups
and 70 to 97% by weight of other ethylenic monomers.
12. A coating composition as claimed in any one of claim 1 to 3 formulated
for use as a basecoat.
13. A coating composition as claimed in claim 12 which contains a metallic
pigment or a pearlescent pigment or a mixture of these.
14. A coating composition as claimed in any one of claims 1 to 3 also
comprising a crosslinker.
15. A coating composition as claimed in any one of claims 1 to 3 which also
comprises a dispersion of different addition polymer microparticles having
C.sub.1-4 alkoxy polyoxyalkylene stabiliser units.
16. A coating composition as claimed in claim 15 which comprises 5 to 95%
by weight said addition polymer microparticles and 95 to 5% by weight of
the different addition polymer microparticles having C.sub.1-4 alkoxy
polyoxyalkylene stabiliser units.
17. A coating composition as claimed in claim 1 which also comprises a
polyurethane resin dispersion.
18. A sprayable aqueous coating composition for motor vehicles comprising
an aqueous dispersion of addition polymer microparticles made by a process
which comprises;
A1) polymerising a mixture of ethylenic monomers comprising a crosslinking
monomer and other ethylenic monomers so as to form a crosslinked addition
polymer,
A2) polymerising in the presence of the polymer from A1 a mixture of
ethylenic monomers comprising at least 10% by weight of monomer having a
solubility in water of less than 0.1% by weight, crosslinking monomer and
optionally other ethylenic monomers,
B) polymerising in the presence of the polymer from (A2) a different
monomer mixture containing 5 to 19% by weight of monomer having acid
groups, optionally monomer having other hydrophillic groups and other
ethylenic monomer so as to form a non-crosslinked stabilising mantle of
polymer containing acid groups, which has a Tg of -50.degree. C. to
+50.degree. C.
19. A process for producing a sprayable aqueous coating composition for
motor vehicles comprising:
A1) polymerising a mixture of ethylenic monomers comprising a crosslinking
monomer and other ethylenic monomers so as to form a crosslinked addition
polymer,
A2) polymerising in the presence of the polymer from (A1) a different
mixture of ethylenic monomers comprising at least 10% by weight of monomer
having a solubility in water of less than 0.1% by weight, crosslinking
monomer and optionally other ethylenic monomers,
B) polymerising in the presence of the polymer from (A2) a different
monomer mixture containing 5 to 19% by weight of monomer having acid
groups, optionally monomer having other hydrophillic groups and other
ethylenic monomer so as to form a non-crosslinked stabilising mantle of
polymer containing acid groups having a Tg of -50.degree. C. to
+50.degree. C.,
so as to form an aqueous dispersion of addition polymer microparticles
having a crosslinked core and a non-crosslinked stabilising mantle.
20. A process of coating a motor vehicle which comprises spraying on to the
surface of the vehicle a layer of an aqueous coating composition
comprising an aqueous dispersion of addition polymer microparticles having
crosslinked core and a non-crosslinked stabilising mantle containing acid
groups, characterised in that the crosslinked core comprises;
i) a crosslinked inner core of an addition polymer and,
ii) a crosslinked outer core of addition polymer which is made from at
least 10% by weight of monomers having a solubility in water of less than
0.1% by weight,
the weight ratio of the inner core to the outer core being in the range
10:90 to 90:10,
and subsequently allowing or causing the layer to dry or cure.
21. A process for applying a basecoat-clear coating to a motor vehicle
which comprises spraying on to the surface of the vehicle a first layer of
an aqueous coating composition comprising an aqueous dispersion of
addition polymer microparticles having a crosslinked core and a
non-crosslinked stabilising mantle containing acid groups, characterised
in that the crosslinked core comprises;
i) a crosslinked inner core of an addition polymer and,
ii) a crosslinked outer core of addition polymer which is made from at
least 10% by weight of monomers having a solubility in water of less than
0.1% by weight,
the weight ratio of the inner core to the outer core being in the range
10:90 to 90:10, followed by
spraying a layer of a clearcoat over this first layer and then causing both
layers to dry or cure together.
Description
This invention relates to an aqueous coating composition and to a process
for preparing the composition. It also relates to a coating process using
the coating composition and to a substrate coated by the coating process.
The painting of motor vehicles broadly involves three stages. The first
stage is called pre-treatment in which the bare metal is treated with
various chemicals to improve corrosion resistance and the adhesion of
subsequently applied paint coatings. In the second stage, one or more
coats of primer and/or surfacer are applied to even out small surface
irregularities and provide a foundation for subsequent layers. In the
final stage, a topcoat is applied. The topcoat gives the vehicle its final
appearance and also must resist the elements and physical damage.
The topcoat on modern motor vehicles, particularly cars, is often applied
using what is known as a basecoat-clearcoat process. This involves
applying two different layers of paint. The first layer is a pigmented
composition called a basecoat which gives the vehicle its colour as well
as any other pigment effects such as a metallic or pearlescent effect. The
second and final layer is an unpigmented composition called a clearcoat
which provides the final glossy appearance.
European Patent EP-B-0 038 127 discloses and claims an entirely
revolutionary waterborne basecoat which can be used in the original
manufacture of motor vehicles. The Patent discloses a pseudoplastic or
thixotropic composition which comprises an aqueous dispersion of acrylic
polymer in water. The dispersed polymer particles are made from various
ethylenic monomers and are internally crosslinked. The combination of the
internal crosslinking and the rheological properties make these basecoats
particularly good for use with metallic pigments. These basecoats give
particularly good metal flake orientation and hence good metallic "flip"
effect, and are very resistant to disturbance by the subsequently applied
clearcoat.
European Patent EP-B-0 300 612 discloses waterborne basecoats comprising
similar dispersions which have a crosslinked core and a non-crosslinked
stabilising mantle having salt forming groups. These dispersions are used
in combination with another different type of dispersion so as to give
basecoats which can be used for the refinishing of motor vehicles.
We have now found that by including in part of the core a minimum
proportion of monomers having a low water solubility, we can produce
waterborne basecoats which, when overcoated with a clearcoat, will form
topcoats having improved resistance to humidity and which have very good
"flip" appearance.
Our new addition polymer microparticles are made by polymerising
ethylenically unsaturated monomers and consist of a crosslinked core from
which there extends a non-crosslinked stabilising mantle containing acid
groups.
According to the present invention there is provided a sprayable aqueous
coating composition for motor vehicles comprising an aqueous dispersion of
addition polymer microparticles having a crosslinked core and a
non-crosslinked stabilising mantle containing acid groups, characterised
in that the crosslinked core comprises;
i) a crosslinked inner core of an addition polymer
ii) a crosslinked outer core of an addition polymer which is made from at
least 10% by weight of monomers having a solubility in water of less than
0.1% by weight,
the weight ratio of the inner core to the outer core being in the range
10:90 to 90:10, preferably 25:75 to 75:25, and the mantle has a Tg of
-50.degree. C. to +50.degree. C.
The outer core preferably surrounds the inner core. The inner and outer
core can have the same monomer composition in which case the crosslinked
core is homogeneous. Preferably the inner and outer core have a different
monomer composition.
The outer core preferably has a Tg of at least 5.degree. C. greater than
that of the inner core, more preferably at least 10.degree. C. greater,
still more preferably at least 20.degree. C. greater and most preferably
at least 40.degree. C. greater.
The outer core preferably has a Tg of greater than 10.degree. C. The inner
core preferably has a Tg of less than -10.degree. C., more preferably less
than -25.degree. C.
The Tg of each portion of the microparticles can be calculated from the
monomers from which that portion is made by using the Fox Equation (in
which Tg is expressed in Kelvin):
##EQU1##
The outer core is made from at least 10% by weight of monomer having a
water solubility of less than 0.1% by weight, crosslinking monomer and
optionally other ethylenic monomer. The outer core is preferably made from
at least 15% by weight of monomer having a water solubility of less than
0.1% by weight, more preferably at least 20%, most preferably at least 40%
and especially above 90%. A particularly preferred outer core is made from
between 95 and 99.5% by weight of monomer having a water solubility of
less than 0.1% by weight and between 0.5 and 5% of crosslinking monomer.
The water solubility of certain monomers is given in J. W. Vanderhoff,
J.Polym.Sci: Polymer Symposium, 72, 161-198 (1985) or F. C. Leonard, Vinyl
& Diene Monomers, Parts I to III, published by John Wiley in their High
Polymers Series in 1970. The water solubility of other monomers can be
determined by preparing a saturated, equilibrated solution of the monomer
in water at 25.degree. C., extracting a sample of the aqueous phase and
determining the monomer concentration by gas chromatography against an
internal standard, for example isopropanol. Examples of monomers having
water solubility of less than 0.1% by weight, with the literature figure
for their solubilities in parentheses, are n-octyl acrylate (0.002%),
dimethyl styrene (0.003%), alpha-methyl styrene (0.005), 2-ethylhexyl
acrylate (0.001), vinyl toluene (0.008%), hexyl acrylate (0.008%), styrene
(0.03%), vinyl hexanoate (0.004) and n-butyl methacrylate (0.03), of which
2-ethylhexyl acrylate and styrene are preferred. Styrene is particularly
preferred because compositions in which the microparticle contains styrene
show particularly good mechanical properties such as chip resistance.
Crosslinking monomers can be monomers having more than one ethylenic
unsaturation which can polymerise with the other monomers so as to
crosslink the polymer. Examples of suitable crosslinking monomers are
allyl methacrylate, vinyl acrylate divinyl benzene, ethylene glycol
dimethacrylate and glycerol triacrylate. The crosslinking monomer can also
be a mixture of two monomers having coreactive functional groups such as
epoxy and carboxyl (for example glycidyl methcarylate and methacrylic
acid), anhydride and hydroxyl or isocyanate and hydroxyl.
Preferably the crosslinking monomer is allyl methacrylate. Preferably the
outer core is made from 0.5 to 5% by weight of crosslinking monomer, more
preferably 1 to 4%.
The other ethylenic monomers which can be included in the outer core have a
water solubility greater than 0.1% by weight. Using the nomenclature
(meth)acrylate to represent acrylate and methacrylate equally and
(meth)acrylic to represent acrylic and methacrylic equally, examples of
other ethylenic monomers are (meth)acrylic acid esters and nitriles and
vinyl esters. Examples of (meth)acrylic acid esters are C.sub.1-5 alkyl
esters, particularly methyl (meth)acrylate, ethyl (meth)acrylate, propyl
(meth)acrylate and butyl acrylate, and poly(ethylene oxide) esters such as
polyethylene glycol methacrylates. Examples of nitriles are
(meth)acrylonitrile. Examples of vinyl esters are vinyl C.sub.1-4
alkanoate esters, particularly vinyl acetate, vinyl propionate and vinyl
butyrate.
Most preferably the other ethylenic monomers are methyl methacrylate and
butyl acrylate.
Most preferably the outer core comprises monomers selected from methyl
methacrylate, butyl acrylate, 2-ethylhexyl acrylate, styrene and allyl
methacrylate and mixtures of these.
The inner core can be made from crosslinking monomer and other ethylenic
monomer, optionally together with monomers having a water solubility of
less than 0.1% by weight.
The crosslinking monomer can be any of those described in relation to the
outer core. Preferably the inner core is made from 0.5 to 5% by weight of
crosslinking monomer.
The other ethylenic monomer can be any of those described in relation to
the outer core. Preferably the inner core is made from 65 to 99.5% by
weight of other ethylenic monomer.
Preferably the inner core is made from less than 30% by weight of monomers
having a water solubility of less than 0.1% by weight, more preferably
less than 25% by weight, and most preferably less than 10% by weight.
These monomers can be any of those referred to above in relation to the
outer core. Most preferably the inner core is made from monomers selected
from methyl methacrylate, butyl acrylate, styrene and allyl methacrylate.
The core in practice consists of a polymer seed onto which the core is
formed. Where the core comprises an inner core and an outer core then the
seed is regarded as part of the inner core.
The polymer seed can be formed from any of those monomers described above
in relation to the monomers making up the core. Preferably the polymer
seed is made from the same monomers as the core. Preferably, when the core
comprises an inner core and an outer core, the seed comprises the same
monomers as the inner core.
Preferably there are no hydrophilic monomers such as hydroxyl or acid
functional monomers in the core because these tend to have a deleterious
effect on water resistance in the final coatings.
The non-crosslinked mantle which is formed on the core contributes wholly
or in part to the stability and rheological properties of the
microparticles in dispersion. This mantle is made from monomer having acid
groups, optionally monomer having other hydrophillic groups, optionally
monomer having a water solubility of less than 0.1% by weight, and other
ethylenic monomer.
Examples of monomers having acid groups are carboxylic acid, phosphate and
sulphonate functional monomers such as (meth)acrylic acid. Preferably the
monomer having acid groups is methacrylic acid.
Examples of monomers having other hydrophillic groups are hydroxy
functional monomers and poly (ethylene oxide) containing monomers.
Examples of hydroxy functional monomers are hydroxyethyl (meth)acrylate,
hydroxybutyl (meth)acrylate and hydroxy propyl (meth)acrylate. A preferred
hydroxy functional monomer is hydroxyethyl acrylate. Examples of poly
(ethylene oxide) containing monomers are those containing a poly (ethylene
oxide) moiety of molecular weight 750 to 2500, for example methoxy poly
(ethylene oxide) 2000 methacrylate in which the 2000 indicates the
molecular weight of the poly (ethylene oxide) moiety.
Examples of monomers having a solubility in water of less than 0.1% by
weight are those monomers referred to as such above in relation to the
outer core. Examples of other ethylenic monomers making up the mantle are
those monomers referred to as such above in relation to the outer core.
Preferred mantle monomers in addition to the monomer having acid groups
are styrene, butyl methacrylate, butyl acrylate and methyl methacrylate.
Typically the mantle is made from 3 to 30%, preferably 5 to 20%, more
preferably 5 to 19%, most preferably 5 to 17% by weight of monomers having
acid groups and 70 to 97%, preferably 80 to 95%, more preferably 81 to 95%
and most preferably 83 to 95% by weight of other ethylenic monomers and
any monomers having a solubility in water of less than 0.1% by weight.
When the mantle is also made from monomers having other hydrophillic
groups these preferably make up from 5 to 35% by weight of the mantle.
The weight ratio of the core to mantle is preferably 5:95 to 95:5, more
preferably 40:60 to 90:10.
Preferably the acid groups on the mantle are at least partially neutralised
by the presence of a base such as an amine, for example dimethyl
aminoethanol, so as to form a salt.
Preferably the microparticles have a diameter of 10 to 500 nm, more
preferably 25 to 200 nm. Preferably the mantle has a Tg of -40 to
+30.degree. C.
The aqueous continuous phase in which the microparticles are dispersed
comprises water, optionally with one or more water miscible organic
solvents. Preferably the aqueous continuous phase comprises at least 50,
more preferably at least 75 and most preferably at least 90 weight %
water. An example of a suitable water miscible solvent is 2-butoxyethanol.
Preferably the microparticle dispersions themselves are pseudoplastic or
thixotropic, more preferably pseudoplastic. Preferably the dispersions
have a low shear viscosity (measured at 22% non-volatile content,
containing 10% 2-butoxy ethanol and at pH 8.0, on a Couvette viscometer at
a shear rate of 1s.sup.-1 and at 25.degree. C.) of more than 0.5 Pa.s, and
a high shear viscosity (measured under the same conditions on a cone and
plate viscometer at a shear rate of 10.sup.4 s.sup.-1 at 25.degree. C.) of
less than 0.1 Pa.s.
The microparticles can be made by the general processes described in EP-B-0
038 127, EP-B-0 001 489 and EP-B-0 300 612. In particular, they can be
made by an emulsion polymerisation process which comprises;
A1) polymerising a mixture of ethylenic monomers comprising a crosslinking
monomer and other ethylenic monomers so as to form a crosslinked addition
polymer and then,
A2) polymerising in the presence of the polymer from A1 a mixture of
ethylenic monomers comprising at least 10% by weight of monomer having a
solubility in water of less than 0.1% by weight, crosslinking monomer and
optionally other ethylenic monomers,
B) polymerising in the presence of the polymer from (A2) a different
monomer mixture containing monomer having acid groups, optionally monomer
having other hydrophillic groups and other ethylenic monomer so as to form
a non-crosslinked stabilising mantle of polymer containing acid groups.
Preferably the monomer mixture in step (A2) produces a polymer having a Tg
of at least 5.degree. C. greater than the Tg of the polymer produced in
(A1).
Preferably step (A1) comprises a first step in which a mixture of ethylenic
monomers optionally comprising a crosslinking monomer is polymerised to
form a polymer seed followed by polymerisation of further ethylenic
monomers comprising crosslinking monomer so as to form the crosslinked
inner core.
Preferably the emulsion polymerisation to form the polymer seed is carried
out by firstly emulsifying the appropriate monomer mixture in water in the
presence of a surfactant, heating this emulsion to a temperature at which
polymerisation will occur in the presence of a polymerisation initiator
and then adding a suitable polymerisation initiator.
Preferably the emulsion polymerisations to form the inner core (A1), the
outer core (A2) and the mantle (B) are carried out by firstly emulsifying
the appropriate monomer mixture in water in the presence of a surfactant,
and then feeding this monomer emulsion into the aqueous dispersion from
the previous stage in the presence of a polymerisation initiator at a
temperature at which polymerisation occurs.
Suitable surfactants include anionic or non-ionic surfactants. Examples of
suitable anionic surfactants are sodium lauryl sulphate, sodium dioctyl
sulphosuccinate, disodium octadecyl sulphosuccinamate and the ammonium
salt of a sulphate ester of a condensate of nonyl phenol and ethylene
oxide. A suitable non-ionic surfactant is the poly(ethylene glycol) ether
of nonyl phenol.
Suitable initiators include peroxides such as hydrogen peroxide and
tertiary butyl hydroperoxide, persulphates such as potassium persulphate
and ammonium persulphate, azo initiators such as azodiisobutyronitrile and
redox initiator combinations such as ascorbic acid and hydrogen peroxide.
Redox initiators have been found to be particularly good for water
resistance. Optionally, metal salts such as iron, chromium or copper salts
can also be added when redox initiators are used.
Preferably no chain transfer agent is present during step (B) and more
preferably no chain transfer agent is used at all in making the
microparticles.
Typically the polymerisation steps are carried out at a temperature of 40
to 98.degree. C., preferably 50 to 90.degree. C.
The acid groups on the mantle are at least partially neutralised by the
addition of a base, during or preferably after the preparation of the
polymer microparticles. Examples of suitable bases are alkali metal
hydroxides and amines.
Amines are preferred. Suitable amines include ammonia and primary,
secondary or tertiary alkylamines such as triethylamine and dimethyl
ethanolamine.
The coating composition preferably comprises the aqueous dispersion as
described above and a pigment.
The pigment can be any pigment or mixture of pigments suitable for use in
an aqueous composition such as a solid colour pigment, a metallic pigment
or a pearlescent pigment. Preferably the pigment is a metallic pigment or
a pearlescent pigment or a mixture of these optionally together with any
other pigment.
The coating composition can also contain co-solvents, for example
2-butoxyethanol to aid coalescence, extenders, biocides, dispersants,
rheological modifiers, and wetting agents.
Coatings can be formulated for the original manufacture or refinishing of
motor vehicles of many different kinds such as automobiles, trucks,
trailers, transport containers and motorcycles. They can also be
formulated for use in other applications such as for coating lawn mowers
and bicycles.
Preferably the coating composition is a motor vehicle basecoat composition.
Basecoat compositions are formulated for use under a clearcoat.
The coating composition can also comprise a crosslinker. Examples of
suitable crosslinkers are polyisocyanates and aminoplast resins such as
melamine formaldehydes and urea formaldehydes.
Where the coating composition is for use as a basecoat in vehicle
refinishing, it is advantageous to include an aqueous dispersion of
different addition polymer microparticles having C.sub.1-4
alkoxypolyoxyalkylene stabiliser units as described in EP-B-0 300 612.
Preferably the composition comprises 5 to 95% by weight, more preferably 15
to 85%, most preferably 40 to 80%, of the crosslinked addition polymer
microparticles of the invention, and 95 to 5% by weight, more preferably
85 to 15%, most preferably 60 to 20%, of the different addition polymer
microparticles having C.sub.1-4 alkoxy polyoxyalkylene stabiliser.
The addition polymer microparticles having C.sub.1-4 alkoxy polyoxyalkylene
stabiliser are optionally crosslinked. The microparticles are made from
polyoxyalkylene group containing monomers, optionally crosslinking
monomers, optionally also monomers having di-C.sub.1-6 alkylamino, hydroxy
or epoxy groups and other ethylenic monomers.
The polyoxyalkylene group containing monomers are C.sub.1-4
alkoxypolyoxyalkylene (meth)acrylate esters. In practice, these have a
molecular weight in the range 700 to 3,000, preferably 1000 to 2500 and
more preferably around 2000. The C.sub.1-4 alkoxy moiety can be methoxy,
ethoxy or propoxy. Preferably it is methoxy.
The alkylene moiety is predominantly ethylene which may contain a
proportion of propylene and/or butylene.
A preferred stabiliser is methoxypolyoxyethylene (2,000) methacrylate.
Preferably the addition polymer microparticles having C.sub.1-4 alkoxy
polyoxyalkylene stabiliser also contain a monomer having epoxy groups,
such as glycidyl methacrylate.
The monomer having epoxy groups can make up to 5 to 50% by weight of the
addition polymer. Preferably they make up 10 to 30% by weight of the
polymer.
The optional crosslinking monomers can be any of those referred to above as
crosslinking monomers in relation to the outer core of the microparticles
having a crosslinked core and a stabilising mantle containing salt-forming
groups. Preferably the polymer contains less than 1% by weight of
crosslinking monomer and preferably it is not crosslinked.
Examples of other ethylenic monomers making up the addition polymer
microparticles having C.sub.1-4 alkoxy polyoxyalkylene stabiliser are
those monomers referred to above in relation to the outer core of the
microparticles having a crosslinked core and a stabilising mantle
containing salt-forming groups as monomer having a solubility in water of
less than 0.1% by weight and also those referred to there as other
ethylenic monomers.
Preferably the other ethylenic monomers making up the addition polymer
microparticles having C.sub.1-4 alkoxy polyoxyalkylene stabiliser are
C.sub.1-6 alkyl acrylate monomers and vinyl benzene derivative monomers
and, more preferably, they are styrene and butyl acrylate. Where these
preferred monomers are used, the polymer preferably consists of 30 to 80%
styrene, (more preferably 40 to 60%) and 20 to 70% butyl acrylate, (more
preferably 40 to 60%).
The exact proportion of monomers making up the polymer microparticles
having C.sub.1-4 alkoxypolyoxyalkylene stabiliser is chosen so as to
obtain the appropriate and desired physical properties in the polymer
produced. The monomers are selected primarily so as to control the Tg or
glass transition temperature. In particular the monomers are selected such
that the theoretical Tg as calculated by the Fox equation is from
-50.degree. C. to +50.degree. C. Preferably it is -10.degree. C. to
+10.degree. C.
Preferably the polymer microparticles having C.sub.1-4
alkoxypolyoxyalkylene stabiliser units have a diameter of 10 to 1000 nm,
more preferably 50 to 500 nm.
The polymer microparticles having C.sub.1-4 alkoxypolyoxyalkylene
stabiliser units can be made by known methods. For example, they can be
made by emulsion polymerisation or by an aqueous dispersion polymerisation
process as described in EP-A-0013478.
The aqueous dispersion of polymer microparticles having C.sub.1-4 alkoxy
polyoxyalkylene stabiliser units can be added to the coating composition
by stirring it in.
The coating compositions of the invention can also comprise a polyurethane
resin dispersion. Aqueous dispersions of polyurethane resin comprise
particles of polyurethane polymer dispersed in an aqueous medium. The
polyurethane polymer has pendent acid groups, and these acid groups are
neutralised in the presence of a base to form anionic groups which
stabilise the dispersion.
The polyurethane can be made by the reaction of a polyisocyanate, a polyol,
a compound having an acid group and optionally a chain extending compound
such as a polyamine or hydrazine.
Polyisocyanates are compounds with more than one isocyanate group. Examples
of suitable diisocyanates are toluene diisocyanate, hexamethylene
diisocyanate, isophorone diisocyanate and dicyclohexyl methane
diisocyanate. Examples of suitable three or more functional isocyanates
are the reaction products of diisocyanates with polyols such as
trimethylol propane, glycerol and pentaerythritol. Many such
polyisocyanates are commercially available for example under the Desmodur
trade mark from Bayer. A preferred polyisocyanate is a mixture of 2,4'-
and 4,4'-dicyclohexyl methane diisocyanate, available as Desmodur W from
Bayer.
Polyols are compounds with more than one hydroxyl group. Examples of
suitable polyols are simple polyols such as those from which the
polyisocyanate can be made, polyester polyols and polyether polyols. A
preferred polyol is a polyester polyol.
The compound having an acid group preferably has an acid group, such as a
carboxylic acid group and two groups which can react with either the
polyisocyanate or the polyol. An example of a group which can react with
the polyol is an isocyanate group. Examples of groups which can react with
the polyisocyanate are hydroxyl groups and amine groups. One example of a
compound having two hydroxyl groups and an acid group is dimethylol
propionic acid.
Examples of polyamines are ethylene diamine, isophorone diamine and
diethylene triamine.
The polyurethane dispersions are generally dispersed using a base which
ionises the acidic groups on the polymer and so stabilises the dispersion.
The base can be an inorganic base, ammonia or an amine. Preferably the
base is an amine.
The polyisocyanate, the compound having an acid group and the polyol can be
reacted together in an organic solvent to produce an isocyanate terminated
prepolymer which can be dispersed in water in the presence of the base and
then chain extended by adding the polyamine. Alternatively, the prepolymer
can be chain extended in solution and then the final polyurethane polymer
can be dispersed in water in the presence of the base.
Examples of commercially available aqueous polyurethane dispersions are
Witcobond 240 from Baxenden Chemical co., Bayhydrol PR135 from Bayer,
Neorez R984 from Zeneca Specialties, Cydrothane HP 1035 from Cyanamid,
Spensol L52 from Spenser-Kellogg, Flexthane 610 from Air Products and
Incorez W830/074 from Industrial Copolymers Ltd.
The coating compositions can be used to coat motor vehicles in a coating
process which comprises applying a layer of the composition to the surface
of the vehicle and subsequently allowing or causing the layer to dry or
cure. When the coating composition is a basecoat composition, a layer of
clearcoat is usually applied over the basecoat.
The clearcoat can be applied after the basecoat has dried or cured.
Alternatively the clearcoat can be applied only a short time after the
basecoat and before the basecoat has fully dried or cured. In this case
both basecoat and clearcoat are dried and cured in a single step. This is
referred to as a "wet-on-wet" process.
The composition can be applied by conventional means such as brushing,
rolling or spraying. Motor vehicles are preferably painted by spraying.
The layer can be allowed or caused to dry or cure either by leaving it at
ambient temperatures or by the use of heat. Preferably the compositions
are allowed or caused to cure at temperatures between 0 and 160.degree. C.
Typically, when the compositions are used for the refinishing of motor
vehicles they are caused or allowed to dry or cure at temperatures between
10 and 70.degree. C. and for the original painting of motor vehicles
between 100 and 200.degree. C., usually 110 to 150.degree. C. The drying
or curing step takes, for example, between 10 minutes and 24 hours
depending on the conditions used and typically between 10 minutes and 5
hours.
Conventional clearcoats which are well known in the art and which are
commercially available can be used.
The invention will now be illustrated by means of the following Examples in
which all parts are by weight;
EXAMPLES
1. Preparation of Aqueous Dispersions 1 to 6; Crosslinked Polymer
Microparticles with Inner and Outer Core and Stabilising Mantle
The following is a general method for Aqueous Dispersions 1 to 6 which uses
the components given in Tables 1 to 3 below. All of Aqueous Dispersions 1
to 6 have an inner and an outer core. Aqueous Dispersions 3, 5 and 6 are
according to the invention, while Aqueous Dispersions 1, 2 and 4 are
comparative.
1.1 Formation of Polymer Seed
The inner core monomers were emulsified in demineralised water in the
presence of surfactant (the ammonium salt of the sulphate ester of a
condensate of nonyl phenol and 20 moles of ethylene oxide sold as Rhodapex
CO436) in the amounts given in Table 1 using a Silverson Homogeniser
(trade mark) for 20 minutes to form the inner core monomer emulsion. 8.8%
by weight of the inner core monomer emulsion was added to a solution of
Rhodapex CO436 (0.228 parts) in demineralised water (24.806 parts)
pre-heated to 80-85.degree. C. in a nitrogen atmosphere with stirring. The
mixture was stirred for 5 minutes and then the initiator solution from
Table 1 was added. This mixture was stirred for 15 minutes to form a
polymer seed.
TABLE 1
______________________________________
Inner Core Monomers
Dispersion
______________________________________
1 2 3
______________________________________
Styrene 0.0 7.925 0.0
2-Ethylhexyl Acrylate
0.0 6.357 0.0
Methyl Methacrylate
2.447 0.0 2.447
Allyl Methacrylate
0.443 0.443 0.443
Butyl Acrylate 11.83 0.0 11.83
Surfactant 0.172 0.172 0.172
Demineralised Water
10.83 10.83 10.83
Initiator
Demineralised Water
1.157 1.157 1.157
Ammonium Persulphate
0.047 0.047 0.047
______________________________________
4 5 6
______________________________________
Styrene 0.0 0.0 2.447
2-Ethylhexyl Acrylate
0.0 0.0 0.0
Methyl Methacrylate
2.447 1.142 0.0
Allyl Methacrylate
0.443 0.201 0.443
Butyl acrylate 11.83 5.374 11.83
Surfactant 0.172 0.079 0.172
Demineralised Water
10.83 4.896 10.83
Initiator
Dimineralised water
1.157 0.868 1.157
Ammonium Persulphate
0.047 0.022 0.047
______________________________________
1.2 Formation of Inner Core
The remainder of the inner core monomer emulsion was fed into the mixture
over 30 minutes at 80-85.degree. C. and the mixture was stirred for a
further hour so as to form the inner core.
1.3 Formation of Outer Core
The outer core monomers were emulsified in demineralised water in the
presence of surfactant (Rhodapex CO436) in the proportions given in Table
2 so as to form the outer core monomer emulsion. The initiator solution
given in Table 2 was added to the inner core dispersion and then the outer
core monomer emulsion was added over 30 minutes. The mixture was stirred
for a further hour so as to form an inner core/outer core dispersion.
TABLE 2
______________________________________
Outer Core Monomers
Dispersion
______________________________________
1 2 3
______________________________________
Styrene 0.0 0.0 7.408
2-Ethylhexyl Acrylate
0.0 0.0 4.373
Methyl Methacrylate
6.523 6.523 0.0
Allyl Methacrylate
0.366 0.366 0.366
Butyl Acrylate 5.257 5.257 0.0
Surfactant 0.142 0.142 0.142
Demineralised Water
8.75 8.75 8.75
Initiator
Demineralised water
1.157 1.157 1.157
Ammonium persulphate
0.039 0.039 0.039
______________________________________
4 5 6
______________________________________
Styrene 0.0 12.293 2.604
2-Ethylhexyl Acrylate
0.0 7.255 0.0
Methyl Methacrylate
6.523 0.0 3.919
Allyl Methacrylate
0.366 0.604 0.366
Butyl Acrylate 5.257 0.0 5.257
Surfactant 0.142 0.236 0.142
Demineralised Water
8.75 14.688 8.75
Initiator
Demineralised Water
1.157 1.447 1.157
Ammonium Persulphate
0.039 0.065 0.039
______________________________________
1.3 Formation of Stabilising Mantle Containing Salt Forming Groups
The mantle monomers given in Table 3 were emulsified in demineralised water
(8.68 parts) in the presence of Rhodapex CO436 (0.141 parts) so as to form
a dispersion of mantle monomers. This dispersion of mantle monomers was
added to the inner core/outer core dispersion over 30 minutes
simultaneously with an initiator solution of ammonium persulphate (0.016
parts) in demineralised water (1.91 parts). The mixture was held at
80-85.degree. C. for one hour. A solution of dimethyl ethanolamine (0.579
parts) in demineralised water (2.06 parts) was added over 20 minutes. The
resulting dispersion was filtered and allowed to cool.
TABLE 3
______________________________________
Mantle Monomers
Dispersion
______________________________________
1 2 3
______________________________________
Styrene 0.0 0.0 0.0
Butyl Methacrylate
0.0 0.0 0.0
Methyl Methacrylate
3.426 3.426 3.426
Hydroxethyl Acrylate
0.792 0.792 0.792
Butyl Acrylate 3.148 3.148 3.148
Methacrylic Acid
0.553 0.553 0.553
______________________________________
4 5 6
______________________________________
Styrene 1.979 1.98 1.389
Butyl Methacrylate
2.376 2.376 0.0
Methyl Methacrylate
0.0 0.0 2.037
Hydroxyethyl Acrylate
0.792 0.792 0.792
Butyl Acrylate 2.218 2.218 3.148
Methacrylic Acid
0.553 0.553 0.553
______________________________________
The product obtained was an aqueous dispersion of polymer particles having
a crosslinked core and a stabilising mantle having at least partially
neutralised acid groups.
2. Silver Basecoat Compositions 1 to 6
Silver Basecoat compositions 1 to 6 were made from Aqueous Dispersions 1 to
6 respectively as follows;
2.1 A solution of alkylarylphosphate ester of the type described in EP-A-0
206 615 (6.069 parts) was made in butoxyethanol (4.862 parts) and
neutralised to pH 7.6 with dimethylamino ethanol (0.345 parts).
2.2 A pigment paste was prepared by stirring an aluminium paste (60% metal
in a hydrocarbon carrier sold under trademark Silberline SS 5245 AR;
27.565 parts) with 2-butoxyethanol (27.565 parts) for 2 hours at room
temperature. The mixture was left to stand over night. The solution from
2.1 above was added and the mixture was stirred for 15 minutes. A melamine
formaldehyde resin (sold under the trademark Beetle BE370; 14.931 parts)
was added followed by a second melamine formaldehyde resin (sold under the
trademark Cymel 325; 18.664 parts) and the mixture was stirred for 15
minutes to form the pigment paste.
2.3 The Crosslinked microparticle dispersions, prepared as in 1 above
(245.614 parts) was added with stirring to the aluminium pigment paste
(100.436 parts) from 2.2 above. 2-butoxy ethanol (41.332 parts) was added.
2.4 Demineralised water, a 10% aqueous dimethylaminoethanol solution in
demineralised water and a 2% by weight Primal ASE 60 (trademark of Rohm &
Haas) solution in demineralised water were added so as to give a final pH
of 8.0 to 8.2, a viscosity of 20-24 poise (as measured on a Couvette
viscometer at 1s.sup.-1 and 20.degree. C.) and a non-volatile solids
content of 16%.
3. Mica-based Green Basecoat Compositions 7 to 12
Mica-based green Basecoat Compositions 7 to 12 were made from Aqueous
Dispersions 1 to 6 respectively as follows;
3.1 To 2-butoxyethanol (76.9 parts) were added sequentially with stirring,
mica pigment (Irodin 9235 WRII; 31.7 parts), dimethylamino ethanol (0.5
parts), latex from 1 above (75 parts), melamine formaldehyde (Cymel 325;
27 parts), melamine formaldehyde (Beetle BE370; 17.3 parts); Latex from 1
above (202.8 parts) and 2-butoxyethanol (52 parts). A millbase comprising
blue and black pigments, melamine formaldehyde resin and solvent (43
parts) was added.
3.2 Demineralised water, a 10% aqueous dimethylaminoethanol solution in
demineralised water and a 2% by weight Primal ASE 60 (trademark of Rohm &
Haas) solution in demineralised water were added so as to give a final pH
of 8.0 to 8.2, a viscosity of 20-24 poise (as measured on a Couvette
viscometer at 1s.sup.-1 and 20.degree. C.) and a non-volatile solids
content of 16%.
4. Application of Basecoat Compositions 1 to 12
4.1 Coating compositions 1 to 12 were applied by spray application on to
pretreated and electrocoated steel panels (ED 5100 from ACT Laboratories
Inc) which had been coated with a surfacer (M330-7139 from IDAC (UK) Ltd).
The spraying was carried out at 60 psi at 20.degree. C. and 65% relative
humidity in two coats to give a basecoat thickness of 12 to 14 .mu.m. The
coated panels were allowed to stand at room temperature for 30 minutes and
were then stored at 80.degree. C. for 10 minutes.
4.2 A layer of a commercially available clearcoat (M190-517 from IDAC (UK)
Ltd) was applied, the coated panel was allowed to stand for 30 minutes at
room temperature and then stoved at 130.degree. C. for 30 minutes.
5. Testing the Coated Panels for Humidity Resistance
The panels from 5 above were tested according to ASTM D4585-92) as follows.
The panels were exposed in a humidity cabinet with the coated side down.
The water vapour in the cabinet was maintained at 60.degree. C. as
measured 2.5 cm from the panel surface. The backs of the panels were
exposed to room temperature so as to induce condensation on the painted
surface. The extent of blistering (ASTM D714-87) was noted after 4 days.
6. Test Results
The test results for compositions 1 to 12 are summarised in Table 4 below.
The numbers relate to the size of the blisters on a scale of 1 to 10 (1
being about 1 cm in diameter and 10 being microscopic) and the letters
refer to the density of blistering on a standard scale from None, VF (Very
Few), F (Few), M (Medium) and MD (Medium Dense) and D (Dense).
TABLE 4
______________________________________
Composition Humidity Test Result
______________________________________
1 (Comparative)
6 M
2 (Comparative)
6 M
3 6 VF
4 (Comparative)
6 M
5 None
6 8 F
7 (Comparative)
10 M
8 (Comparative)
8 MD
9 8 VF
10 (Comparative)
8 D
11 None
12 8 F
______________________________________
7. Preparation of Aqueous Dispersions 7 and 8 Having a Homogeneous Core
The general method given below was used to make Aqueous Dispersions 7 and 8
which use the components given in Tables 5 and 6 below. Aqueous
dispersions 7 and 8 both have a homogeneous core. Aqueous Dispersion 7 is
according to the invention, while Aqueous Dispersion 8 is comparative.
7.1 Formation of Polymer Seed
Methyl methacrylate (0.542 parts) and butyl acrylate (0.585 parts) were
added to a solution of Rhodapex CO436 (0.250 parts) in dimeralised water
(46.677 parts) pre-heated to 80-85.degree. C. in a nitrogen atmosphere
with stirring. The mixture was stirred for 5 minutes and then an initiator
solution comprising demineralised water (0.583 parts) and ammonium
persulphate (0.017 parts) was added. This mixture was stirred for 15
minutes to form a polymer seed.
7.2 Formation of core
The core monomers given in Table 5 were emulsified in demineralised water
(11.870 parts) in the presence of surfactant (the ammonium salt of the
sulphate ester of a condensate of nonyl phenol and 20 moles of ethylene
oxide sold as Rhodapex CO436; 0.163 parts) using a Silverson Homogeniser
(trade mark) for 20 minutes to form the core monomer emulsion.
TABLE 5
______________________________________
Dispersion
Core Monomers 7 8
______________________________________
Styrene 10.179 0.0
2-Ethylhexyl Acrylate
8.105 0.0
Methyl Methacrylate
0.0 8.864
Allyl Methacrylate 0.601 0.601
Butyl Acrylate 0.0 9.42
______________________________________
The core monomer emulsion was fed into the mixture along with an initiator
mixture of demineralised water (4.33 parts) and ammonium persulphate
(0.034 parts) over 30 minutes at 80-85.degree. C. and the mixture was
stirred for a further hour so as to form the core.
7.3 Formation of Stabilising Mantle Containing Salt Forming Groups
The mantle monomers given in Table 6 were emulsified in demineralised water
(6.571 parts) in the presence of Rhodapex CO436 (0.102 parts) so as to
form a dispersion of mantle monomers.
TABLE 6
______________________________________
Dispersion
Mantle Monomers 7 8
______________________________________
Hydroxethyl Acrylate
1.178 1.178
Butyl Acrylate 3.887 3.887
Methacrylic Acid 0.824 0.824
______________________________________
The dispersion of mantle monomers was added to the core dispersion over 30
minutes simultaneously with an initiator solution of ammonium persulphate
(0.016 parts) and borax (0.014 parts) in demineralised water (0.519
parts). The mixture was held at 80-85.degree. C. for one hour. A solution
of dimethyl ethanolamine (0.488 parts) in demineralised water (2.464
parts) was added over 20 minutes. The resulting dispersion was filtered
and allowed to cool.
The product obtained was an aqueous dispersion of polymer particles having
a crosslinked core and a stabilising mantle having at least partially
neutralised acid groups.
8. Preparation of Comparative Dispersion 9 According to EP-A-0 348 565
Example 34 of EP-A-0 348 565 was repeated as comparative dispersion 9;
6.6% Of Monomer emulsion 1 listed in Table 7 below was added to a stirred
mixture of deionised water (1020 g), sodium lauryl sulphate (1.69 g) and
of dibasic ammonium phosphate (0.9 g) at 81.degree. C. under nitrogen. A
mixture of ammonium persulphate (1.1 g) and deionised water (28 g) was
added and the mixture stirred for 17 minutes. The remainder of monomer
emulsion 1 in Table 7 was added slowly over 72 minutes along with Cofeed 1
from Table 7 maintaining the mixture at about 81.degree. C. The mixture
was stirred for a further 20 minutes at 81.degree. C. and a solution of
ammonium persulphate (1.1 g) in deionised water (55 g) was added over a 10
minute period. Monomer emulsion 2 from table 7 was added over a period of
108 minutes while cofeed 2 from Table 7 was added over 138 minutes at
81.degree. C.
The dispersion was neutralised by adding a solution of basic ammonium
phosphate (24.4) in deionised water (632 g) over 10 minutes followed by a
solution of 28% aqueous ammonia (193 g) in deionised water (200 g).
TABLE 7
______________________________________
Monomer Emulsion 1
Monomer Emulsion 2
______________________________________
Deionised water
150 216
Sodium lauryl
5.4 3.3
sulphate
styrene 425.25 --
allyl methacrylate
22.5 --
methacrylic acid
2.25 235.25
n-dodecylmercaptan
-- 40.5
methylmethacrylate
-- 438.75
______________________________________
Cofeed 1 Cofeed 2
______________________________________
deionised water
77.0 115.0
ammonium 0.44 1.49
persulphate
______________________________________
9. Preparation of Comparative Dispersion 10 according to EP-A-0 348 565
Example 47 of EP-A-0 348 565 was repeated as comparative dispersions 10.
40 g of Monomer Emulsion 1 listed in Table 8 below was added to deionised
water (1102 g) with stirring at 81.degree. C. under nitrogen. A mixture of
ammonium persulphate (1.1 g) and deionised water was added and the mixture
stirred for 17 minutes. The remainder of Monomer Emulsion 1 from Table 8
was added over over 135 minutes along with cofeed 1 in Table 8, at
81.degree. C. under nitrogen. The mixture was stirred for 30 minutes at
81.degree. C. Monomer mixture 2 from table 8 was added over a period of 45
minutes while cofeed 2 from Table 7 was added over 75 minutes at
81.degree. C.
The dispersion was neutralised to pH 8.5 by adding a solution of 28%
aqueous ammonia in deionised water.
TABLE 8
______________________________________
Monomer Emulsion 1
Monomer Emulsion 2
______________________________________
Deionised water
405 75
Sodium lauryl
12.37 2.07
sulphate
2-ethylhexyl
433 --
acrylate
allyl methacrylate
37 --
methacrylic acid
6.2 82.5
n-octyl mercaptan
-- 12.4
methylmethacrylate
761 330
______________________________________
Cofeed 1 Cofeed 2
______________________________________
deionised water
240 135
ammonium 2.92 1.65
persulphate
______________________________________
10. Silver Basecoat Compositions 13 to 16
Silver Basecoat compositions 13 to 16 were made from Aqueous Dispersions 7
to 10 respectively using the same general method as silver basecoats 1 to
6 as follows:
10.1 A solution of alkylarylphosphate ester of the type described in EP-A-0
206 615 (6.069 parts) was made in butoxyethanol (4.862 parts) and
neutralised to pH 7.6 with dimethylamino ethanol (0.345 parts).
10.2 A pigment paste was prepared by stirring an aluminium paste (60% metal
in a hydrocarbon carrier sold under trademark Silberline SS 5245 AR;
27.565 parts) with 2-butoxyethanol (27.565 parts) for 2 hours at room
temperature. The mixture was left to stand over night. The solution from
10.1 above was added and the mixture was stirred for 15 minutes. A
melamine formaldehyde resin (sold under the trademark Beetle BE370; 14.931
parts) was added followed by a second melamine formaldehyde resin (sold
under the trademark Cymel 325; 18.664 parts) and the mixture was stirred
for 15 minutes to form the pigment paste.
10.3 The Crosslinked microparticle dispersions, prepared as in 7 to 9 above
(245.614 parts) were added with stirring to the aluminium pigment paste
(100.436 parts) from 10.2 above. 2-butoxy ethanol (41.332 parts) was
added.
10.4 Demineralised water, a 10% aqueous dimethylaminoethanol solution in
demineralised water and a 2% by weight Primal ASE 60 (trademark of Rohm &
Haas) solution in demineralised water were added so as to give a final pH
of 8.0 to 8.2, a viscosity of 20-24 poise (as measured on a Couvette
viscometer at 1s.sup.-1 and 20.degree. C.) and a non-volatile solids
content of 16%.
11. Application and testing of Silver Basecoat Compositions 1 to 6 and 13
to 16
A comparative test was carried out of basecoat compositions 1 to 6 and 13
to 16 as follows. Compositions 1 to 6 and 13 to 16 were applied to steel
panels, and clearcoated in exactly the same way as given in paragraphs 4.1
and 4.2 above. The panels were tested for humidity resistance in exactly
the same way as in paragraph 5 above.
12. Test Results
The test results for compositions 1 to 6 and 13 to 16 are summarised in
Table 9 below. The numbers relate to the size of the blisters on a scale
of 1 to 10 as referred to in paragraph 6 above and the letters refer to
the density of blistering on a standard scale from None, VF (Very Few), F
(Few), M (Medium) and MD (Medium Dense) and D (Dense). In the table (C)
indicates comparative compositions.
TABLE 9
______________________________________
Silver Basecoat
Rating
______________________________________
1 (C) 8 M/F
2 (C) 9 F
3 10 VVF
4 (C) 9 M
5 10 VVF
6 10 VF
13 10 VF
14 (C) 8-9 M
15 (C) 2 D
16 (C) 2 D
______________________________________
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